1. Field of the Invention
The present invention relates to a stepper motor controlling apparatus and a pen recorder using the same and, more particularly, a stepper motor controlling apparatus for use in closed loop control using an encoder and a pen recorder using the same.
2. Description of the Related Art
The stepper motor can carry out the open loop control based on the pulse signal, and a rotation angle of the motor agrees with an input pulse number. However, in the operation executed under the open loop control, in some cases a displacement is caused due to the out of step at the time of high-speed rotation. Therefore, in order to deal with this problem, the controlling apparatus for carrying out the closed loop control by using the stepper motor to which an encoder is attached has been proposed in the related art.
FIG. 8 is a configurative view of a stepper motor controlling apparatus in the related art. In FIG. 8, an encoder disk 2 with five blades is fitted to a motor shaft of a stepper motor 1 by the press fitting to have a predetermined relation with a motor excitation position. A rotation of this encoder disk 2 is sensed by two photo sensors 3a, 3b. Output signals of the photo sensors 3a, 3b are input into an encoder circuit 4, and the rotation direction and the number of revolution of the encoder disk 2 are sensed. Therefore, an absolute position of a moving object (not shown) that moves in response to the rotation of the stepper motor 1 can be sensed. An output signal of the encoder circuit 4 is input into a digital circuit 5 prepared as an ASIC. The digital circuit 5 executes the closed loop control in such a manner that the stepper motor 1 is rotated/driven in a predetermined direction to eliminate a difference (deviation) between absolute position data of the moving object input from the encoder circuit 4 and positioning data input from a CPU 6.
In the pen recorder, for example, the pen position control is executed by the servo system under closed loop control using the stepper motor to which an encoder is attached. That is, a measuring/recording signal is converted into digital data by an A/D converter (not shown) and input into the CPU 6. The CPU 6 generates positioning data in response to a magnitude of a value of the measuring/recording signal and inputs the data into the digital circuit 5. The present position data of the pen is also input into the digital circuit 5 via the encoder circuit 4. The digital circuit 5 inputs a two-phase excitation signal into a driver 7 to drive the stepper motor 1 in the two-phase excitation system, and executes the position control such that the pen as the moving object is moved to follow up the positioning data that responds to the magnitude of the value of the measuring/recording signal. Accordingly, a changing condition of the measuring/recording signal is recorded as a continuous line segment by the pen on a recording paper.
As the stepper motor drive system capable of switching the two-phase excitation drive and the micro step drive smoothly at a high speed, there was the system set forth in JP-A-8-149892, for example.
Also, as the stepper motor controlling apparatus capable of realizing high-precision positioning, high-speed transfer, and small oscillation characteristic of the stepper motor, there was the system set forth in JP-A-10-150798, for example.
JP-A-8-149892 and JP-A-10-150798 are referred to as related art.
However, following problems lay in the related art shown in FIG. 8.
In case the stepper motor is driven under the closed loop control while sensing the position of the motor by the encoder, the motor driving pulse is generated from the encoder position sensing pulse generated by the closed loop control. As a result, the motor driving circuit becomes simple but it is impossible to execute the speed control.
Also, in the case of the two-phase excitation drive, the motor makes a step-like motion when viewed microscopically. As a result, the rotation of the motor is not smooth and thus it is impossible to move smoothly the moving object.